Power-on reset (POR) circuits are incorporated into integrated circuits to set the IC to a known state at power-up and power-down (or power interruption). POR circuits transition the IC between a reset state with POR active, and an operational state with POR inactive.
For power-up, the POR circuit transitions out-of-reset when supplied power (Vdd) has ramped enough to support stable register operation. When the POR circuit transitions out-of-reset, registers in the digital domain are set to their desired state for operation.
For power-down, the POR circuit transitions into-reset when supplied power (VDD) drops below a safe voltage to retain register values. When the POR circuit transitions into-reset, all registers are reset to a default state.